A Comprehensive Formulation of Aqueous Electrolytes for Low‐Temperature Supercapacitors

Safer‐by‐design and sustainable energy storage devices are envisioned to be among the required 2.0 solutions to satisfy the fast growing energy demands. Responding to this evolution cannot be freed from a global and synergetic approach to design the requisite electrolytes taking into account the toxicity, the eco‐compatibility and the cost of their constituents. To target low‐temperature applications, a non‐toxic and cost‐efficient eutectic system comprising LiNO3 in water with 1,3‐propylene glycol as co‐solvent was selected to design a ternary electrolyte with a wide liquid range. By using this electrolyte in an electrochemical double‐layer capacitor (EDLC), the operating voltage of the device reaches an optimum of 2.0 V at −40 °C over more than 100 h of floating. Moreover, after being set up at 20 °C, the temperature resilience of the capacitance is near total, demonstrating thus a promising feature related to the suitable thermal and electrochemical behaviours of the tested EDLC devices. Safe by design: Electrochemical energy storage devices require a global and synergetic approach to design safer‐by‐design and sustainable electrolytes. An unprecedented strategy is devised taking into account their toxicity, eco‐compatibility and cost while targeting low‐temperature applications by obtaining a ternary electrolyte based on a eutectic system LiNO3 in water.